iPhone PHONE doesn't work

Activated my iPhone over the landline after they asked for my IMEI and ICCID numbers. They said the phone would work within 24hrs but it's way over that and almost a week since I've had the phone with the SIM inserted, during which the iPhone constantly signals that it is healthily connected to the 3 network. Wi-fi is fine. Have tried resetting the phone, resetting the network settings, reinserting the SIM, etc., but whenever a call is attempted this message appears: "Sorry, you've not been given access to this service." The phone can't receive calls either and cellular data is 0 across the board. Thanks for any help.